Self-excited alternating current machine



Jan. 31, 1939. T E. M DOWELL SELF-EXCITED ALTERNATING CURRENT MACHINEOriginal Filed March 27, 1935 E M E17 UR %0///asZ jZo1zfe//.

Patented Jan. 31, 1939 I V r i UNITED STATES PATENT OFFICE 2,145,424SELF-EXCITED ALTERNATIN G CURRENT MACHINE Thomas E. McDowell, Chicago,Ill., assignor to The Pyle-National Company, Chicago, 111., acorporation of New Jersey Original application March 27, 1935, SerialNo. 13,190. Divided and this application July 13, 1936, Serial No.90,274

2 Claims. (Cl. 171-119) The present invention relates in general totionary alternating current armature coils, direct alternating currentmachines, and is principally current field coils, and a simple toothedrotor concerned with the provision of improved means without windings.The alternating current for excitation of the field coils of themachine. armature coils are arranged for connection to a 5 The inventiondescribed herein constitutes a delivery circuit, and the direct currentfield coils 5 division of my copending application Serial No. arearranged to be excited through a suitable 13,190, filed March 27, 1935.rectifier from the alternating current delivery The present invention isparticularly adapted circuit. for use in train lighting systems, andespecially Since, in the above arrangement, the generfor the furnishingof power for the headlight ator will build up from its residual field,it is 10 of the locomotive. On the other hand, it will preferred that arectifier of the cold type be be appreciated bythose skilled in the artthat utilized for furnishing direct current to the field. it may withequal facility be utilized for other It has been found that the copperoxide, elecpurposes where the generation of electricity is trolytic, andother similar types of rectifiers are required, and moreover, althoughthe invention is admirably adapted for this purpose. Where the 15disclosed as being embodied in a single phase generator, as in thiscase, is built up from reapparatus, it is contemplated that theprinciples sidual, the thermionic or vacuum tube type of of theinvention may likewise be embodied in rectifier would be inoperativeuntil the rated voltapparatus adapted for multiphase operation. age wasapplied, unless the filament were heated 0 Heretoiore, direct currentgenerators operated at the start, which of course would be impracby asuitable prime mover have been used for tical. However, the presentinvention contemfurnishing power to the headlights of locomoplates thatduring the initial period of generatives, and while these machines hadvery detion a cold type of rectifier, such as the copper sirableoperating characteristics, they were par oxide type, may be used, andautomatic switching ticularly objectionable from the standpoint of meansprovided for subsequently throwing the 26 maintenance and servicing,since the direct curexcitation to a rectifier of the thermionic or rentgenerators necessitated the use of brushes. vacuum tube type.

These brushes, due to wear, oftentimes required As an added feature ofthe invention, the above replacement under conditions where skilled orarrangement for exciting the field is admirably 30 suitable labor eitherwas not present or not adapted to effect compound or shunt operating soreadily obtainable. characteristics, as desired. For compound char- Toovercome this disadvantage and other obacteristics, it is proposed toprovide in the transjections, attempts were made to utilize alterformerfor the running rectifier a potential prinating current generators, andin order to get mary winding and also a current primary windaway fromthe use of brushes, exciters, etc., the ing, the potential winding beingconnected 35 field coils were replaced by permanent magnets. across thedelivery circuit, whereas the series The disadvantage of thisarrangement was that winding is connected in the delivery circuit, sothe regulation efficiency of the machine was mathat the load currentpasses therethrough. The terially decreased as it became loaded.secondary coil of the transformer is connected The present inventionseeks to provide an alterto the supply side of the rectifier. It willthere- 40 hating current machine which is self-excited, fore be evidentthat as the load changes the exthus doing away with the use of brushesand citation of the direct current field will be inseparate exciters;amachine embodying the opercreased an amount determined by the design ofating advantages of a direct current generator; the transformerwindings. Without the series a generator which is simplein'construction, beprimary winding of the transformer, the char- 45 ingdevoid of a large number of moving parts; acteristics will be similar toa direct current and which may be simply and easily arranged togenerator of the shunt type. have shunt or compound characteristics, asde- Although the invention is disclosed primarily sired, to the end thatits characteristics may be in connection with a generator, it iscontemplated 5O readily varied to meet diiferent operating conthat itmay also be embodied in certain'types oi ditions of load. alternatingcurrent motors.

In accordance with the general features of the Other objects andfeatures of the invention will invention, it is proposed to provide, inthe premore fully appear from the following detailed ferred form of theinvention, an alternating curdescription, taken in connection with theaccomrent generator of the inductor type, having stapanying drawing.

. single phase, but it will The drawing diagrammatically illustrates theinvention as applied to an inductor type generator, and switching meansfor automatically transferring, the field excitation from one type ofrectifier to a different type of rectifier.

As shown-on the drawing:

'In the illustrated embodiment of the invention as shown, the inventionis disclosed as embodying an alternating current generator of the in-'ductor type, and including a toothed rotor H) which is devoid ofwindings, and a stator having alternating current coils and directcurrent coils |2-|2.

.While it is not primarily essential to the practice of the presentinvention that the foregoing type of generator be utilized, an inductortype generator is preferred, since there are no rotatable parts carryingwindings which might be subject to damage due to centrifugal action, andthis type of generator is, moreover, devoid of brushes which would haveto be replaced from time to time as they become worn.

The alternating current coils ||-|l, and these coils are connected tofeed a delivery circuit, indicated at |3; This circuit in'the' presentinstance'is shown as being be obvious that a multiphase delivery circuitmay be used with equal facility, without interfering in any manner withthe practice of the present invention.

For exciting the field winding, it is proposed to utilize a rectifierwhich may be fed-or energized from the alternating current deliverycircuit of the generator. Since, in the proposed arrangement, thegenerator will have to build up from residual field magnetism, it ispreferable to use a rectifier of the cold type, such as the copper oxidetype, electrolytic type, and other similar types. Of course, once thegenerator has built up, it may be desirable under certain conditions to'then supply the excitation from a hot type of rectifier, such as thethermionic or vac uum tube type. The vacuum tube type, containing aheated filament, is not desirable for initial building up of thegenerator, since the generator output is very low, and it requires sometime for the filament of thetube rectifier to be heated sufficiently tofunction properly.

In the embodiment of the invention as shown, initial excitation of thefield coils |2-|2 is accomplished by a bridge rectifier, as shown at I,this rectifier being of, the cold type. The rectifier I4 is energizedfrom the secondary winding l5 of the transformer l6 having a primarycoil l1 which is connected across the delivery circuit l3 of thegenerator. Of course, if the delivery voltage of the generator issufficiently low, this rectifier may be connected directly to thedelivery circuit,

. without using a transformer.

For subsequently exciting the coils |2-|2, after the generator has builtup, there is provided a rectifier of the hot or thermionic type whichcomprises a rectifier tube l8 which is provided with two anodes I9 andand the usual filament 2|.

This rectifier is energized from a transformer 22 having a primarycomposed of a voltage winding 23 and a current winding 23, the formerbeing connected across the delivery circuit l3 of the generator-and thelatter in series therein. The secondary of the transformer 22 isprovided with two windings, namely, a, winding 24 which has itsterminals respectively connected to the anodes I9 and 20 'of therectifier tube, and a winding 25 which has its end terminals connectedto the filament 2|. Output from the rectifier is obtained is generatedin the through conductors 26 and 21,'which are respectively connected tothe mid-points of windings 24 and 25.

For automatically transferringthe excitation from the rectifier ll torectifier tube 18, thereis provided a'relay 28 having normally closed.contacts 29 and normally opened contacts 30. The relay is actuated bymeans of a coil 3|, which in' this instance is a potential coilconnected across the delivery circuit |3 and arranged to operate therelay when a predetermined value of potential across the deliverycircuit is reached. It is obvious that the operating coil of this relaymay be designed to operate on current rather than voltage, and may be.energized'in response to some other characteristic of the generator; forexample, the coil could be in the field circuit and arranged to operatethe relay when the field current reaches a predetermined value.

In its normal position, contacts 29.. are closed, and are so arranged asto close the energizing circuit of rectifier H from the secondarywinding |5 of its associated transformer; Whenthe generator has built upso as to supply a predetermined potential on the delivery circuit, therelay operates to close contacts '30, which are in the output circuit ofthe rectifier tube I8, this action at the same time disconnecting theenergizing cir- The series winding 23" of the supply transformer for therectifier used during normal operation of the generator will vary theexcitation of the ternating current machine which is self-excited,

doing away with the use of brushes and a separate exciter; whichembodies the operating advantages of direct current generators; which issimple in construction and devoid of a large number of moving parts;which may be simply and easily arranged to have shunt or compoundcharacteristics, as desired, and which is so arranged that itsfieldwinding may be initially excited through rectifying means having certaincharacteristics,

and thereafter through rectifying means having differentcharacteristics.

I claim as my invention:

1. In combination, an alternator having a field structure, a fieldwinding, and an armature winding, a first field excitation means adaptedto functionwith the voltage due to the residual magnetism ofthe fieldstructure to build up the field magnetism, said first excitation meanscomprising a rectifier of the cold type connected with said armaturewinding and with said field winding, a second field excitation meansadapted to function after the excitation has been materially'increasedby said first excitation means, said second excitation means having afilament connected with said armature to be heated as the alternatorbuilds up its voltage,'said second excitation means comprising athermionicrectifier nator to transfer the excitation duty from saidfirst to said second excitation means.

2. In combination, an alternator having a-field structure, a directcurrent field winding, and an armature winding, a first field excitationmeans adapted to function with the voltage due to the residual magnetismof the field structure to build up the field magnetism, said firstexcitation means comprising a rectifier of the cold type connected withsaid armature winding and with said field winding, a second fieldexcitation means connectible with said armature and said field windingand adapted to function after the excitation has been materiallyincreased by said first excisaid armature.

THOMAS E. McDOWELL.

